The present invention relates to a method for making punches and more particularly to a method of making sintered carbide punches using multi layer ceramic technology.
Multi-layer ceramic technology is used in the present invention for making punches for semiconductor packaging.
Various techniques have been employed for forming a multi layer substrate. For example, U.S. Pat. No. 5,779,833 describes a method for manufacturing an integral three dimensional object from laminations, including the steps of fabricating a plurality of greensheet layers and firing the same to remove binder material.
For the substrate structure, U.S. Pat. No. 5,011,725 discloses substrates with dense material vias derived from a metallization composition, wherein plated through holes are made in ceramic substrates. The holes are infiltrated with another metal for strength. In particular, U.S. Pat. No. 5,530,081 describes a plastic material composed of silicon carbide, polycarbosilane and organic solvent and the use of ceramic carbide material for forming a molded object.
The present invention provides a method for making carbide punches using multi-layer ceramic (MLC) technology, comprising the steps of preparing a sublaminate of greensheets, patterning through-holes by drilling out the holes, filling the holes with a carbide material, sintering the same at high temperature and removing non-carbide material to produce punches.
In a conventional method of fabricating a ceramic multi layer substrate by greensheet fabrication technology, a ceramic slurry is cast on a carrier film and the resulting ceramic greensheet is separated from the carrier film followed by subsequent fabrication processes. Further, the ceramic greensheets tend to be deformed during the process of punching holes and the process of filling with paste, resulting in misalignment of the holes in a stack of the greensheet U.S. Pat. No. 5,271,150 has been suggested to relieve the above-mentioned problem and is directed to a method of forming a ceramic multi layer substrate, wherein an organic film is bonded on a greensheet. Through-holes are formed on the greensheet and filled with conductive paste. One of the films is removed and a laminate assembly is formed. However, none of the conventional techniques describe a method for making small punches at low cost by utilizing multi layer ceramic (MLC) technology.
It is therefore an object of the present invention to provide a method for making small punches using multi-layer ceramic (MLC) fabrication technology. The punches made according to the present invention have dimensions of two (2) to ten (10) mils in diameter and approximately hundred (100) mils in lengths. The small punches of the present invention are used for fabricating semiconductor packaging. The alternative at present is tungsten carbide cermet punch which is precision ground from 125 mil diameter stock and is costly, whereas the cost of manufacturing a punch according to the invention, is at least an order of magnitude less.
Another object of the present invention is to provide a method for making a punch array in a single step. This can be achieved by simultaneously sintering punches while they are in intimate contact with a base plate. This array can subsequently be used to punch an array of vias in a greensheet. The present invention therefore eliminates the additional step of loading individual punches into a punch head. Accordingly, the present invention offers both cost and time savings.
A further object of the present invention is to provide a large number of small punches made in parallel to precise dimensions by utilizing MLC technology.
These and other objects of the present invention, which shall become herein apparent, are achieved by a method of making punches using multi-layer ceramic technology, comprising the steps of:
(a) preparing a sublaminate matrix or a single thick green sheet of a high or low sintering temperature material;
(b) drilling holes in the sublaminate optionally using a mask as a guide;
(c) filling the holes with punch material paste utilizing the solupor process or a process that ensures complete via fill and produces a flush surface after paste drying;
(d) laminating the sublaminate to a base plate or as a freestanding substrate;
(e) firing a laminate at an appropriate sintering temperature; and
(f) removing the matrix material by a chemical or mechanical method.
Instead of a sublaminate in process (a), alternatively a single thick green sheet can also be used. Further, the flush surface in the filling process (c) does not have any depression or dimples.